1. Field of the Invention
This invention relates generally to large area array monitoring or imaging systems of the type used for ultrasound or x-ray analysis and, more particularly, to systems and methods which combine high density transducer arrays with processing circuitry.
2. Background Art
Ultrasound monitoring and imaging systems use transducer arrays to create short high frequency acoustic pulses which undergo reflection from surface interfaces at which there are changes in acoustic impedance. The transducers convert reflected energy into electrical signals which are processed to generate two-dimensional or three-dimensional image information descriptive of a subject under study.
Acoustic transducer cells are typically multi-layered structures comprising piezoelectric or micro-machined transducers configured with electronic circuitry in a probe assembly. The electrical signals are further processed by beam forming circuitry, typically external to the probe assembly, to generate and display images of structures being studied.
It is desirable for ultrasound probes to contain a portion of the beam forming circuitry integrated with the transducer array, as this can reduce complexities and potentially adverse effects which may result from connecting cables between the transducer probe and an external system that provides signal processing and control functions. For example, with connecting cables extending over distances on the order of several meters significant capacitance effects can arise. Furthermore, signals received from the transducer assembly may be weak, subject to RF interference and may exhibit an undesirably low S/N ratio. To mitigate these effects, front-end circuit cells providing, for example, amplification, pulse generation, and transmit/receive switching, can be integrated with a transducer array.
Transducer arrays in ultrasound probe assemblies typically span an area of about 20 cm2. For new medical applications, such as screening for internal bleeding and tumors, much larger arrays, on the order of 300 cm2, are required. In non-medical applications even larger arrays may be desired.
Such large arrays may be formed by tiling of a large number of transducer modules in rows and columns. Each transducer module comprises a subarray of transducer cells and an integrated circuit coupled to the subarray. Performance of large transducer area is significantly degraded when there are significant variations in spacings between modules.